Water quality standards

Water quality standards:

  • Protect water resources for uses such as fishing, swimming and other recreation, and sustaining fish, bugs, plants, and other aquatic life
  • Are a measure to identify polluted waters or healthy waters in need of protection
  • Guide the limits set on what regulated facilities can discharge to surface water

The federal Clean Water Act requires states to designate beneficial uses for all waters and develop water quality standards to protect each use. Water quality standards consist of several parts:

  • Beneficial uses — Identify how people, aquatic communities, and wildlife use our waters
  • Numeric standards — Amounts of specific pollutants allowed in a body of water and still protects it for the beneficial uses
  • Narrative standards — Statements of unacceptable conditions in and on the water
  • Antidegradation protections — Extra protection for high-quality or unique waters and existing uses

Together, the beneficial uses, numeric and narrative standards, and antidegradation protections provide the framework for achieving Clean Water Act goals. The Clean Water Act specifies healthy aquatic life and recreation as beneficial uses. Others that are protected in Minnesota's rules are:

  • Drinking water
  • Industrial and agricultural uses
  • Wildlife
  • Navigation
  • Aesthetic enjoyment

Minnesota’s water quality standards are provided in Minnesota Rules chapters 7050 (Waters of the State), and 7052 (Lake Superior Basin Water Standards). Details of how water quality standards are implemented in point-source discharge permitting are contained in Minnesota Rules chapter 7053 (State Waters Discharge Restrictions), and parts of chapter 7052.

All current state water rules administered by the MPCA are available on the Minnesota water rules page.

Current water standard projects and priorities

The MPCA is continually working to revise, develop, or otherwise improve Minnesota’s water quality standards. The process for developing and codifying water quality standards can take months and often takes years. The agency must establish the technical basis and create supporting documents for the standard, ensure peer review, and give the public the opportunity to comment on their proposal. The U.S. Environmental Protection Agency has final authority to approve or disapprove any new or revised standards.

PDF icon Inventory of water quality standards projects, 2018-2020 (wq-s6-35)

Overview and status of water quality standards projects the MPCA has prioritized for 2018 to 2020. The inventory reflects the priorities identified in 2017 triennial. The inventory is updated every year by December 15.

More information about the expected development of these water quality standards is available in the work plan for 2018 to 2020. The rulemaking docket has more information about the status of water quality standards projects in rulemaking (Group 1 in the inventory): PDF icon Public Rulemaking Docket (mm-rule1-00)

Elements of standards

Water quality standards are the fundamental regulatory and policy foundation to preserve and restore the quality of all waters of the state. They consist of three elements:

  • Classifying waters with designated beneficial uses;
  • Narrative and numeric standards to protect those uses; and
  • Nondegradation (antidegradation) policies to maintain and protect existing uses and high quality waters.

Beneficial uses

In Minnesota's water quality standards, all groundwater is protected as a source of drinking water (Class 1). All surface waters are classified and protected for multiple beneficial uses. These uses encompass the benefits and uses of surface waters as listed in Minn. R. ch. 7050 and summarized below. Note: The use class numbers 1-7 are not intended to imply a priority rank to the uses.

Use class

Beneficial use

Class 1

Domestic consumption

Class 2

Aquatic life and recreation

Class 3

Industrial consumption

Class 4

Agricultural and wildlife

Class 5

Aesthetics and navigation

Class 6

Other uses

Class 7

Limited Resource Value Water (LRVW)

Minnesota adopted a framework that includes broad uses for domestic consumption, aquatic life, recreation, industry, agriculture, navigation and aesthetic enjoyment. Groundwater has one beneficial use, domestic consumption. Surface waters have multiple beneficial uses that are reflected in the standards. Waters determined not to attain aquatic life and recreational uses are reclassified as “limited resource value waters,” and have modified standards, but are still protective for downstream waters and other beneficial uses.


A narrative water quality standard is a statement that prohibits unacceptable conditions in or upon the water. Narrative standards that address very fundamental and basic forms of water pollution, such as floating solids, scums, visible oil film, or nuisance algae blooms are also referred to as “free froms.” Whereas, other narrative standards set water quality goals for more defined pollutants to protect surface waters and aquatic biota from:

  • eutrophication
  • impairment of the biological community
  • impairment of fish for human consumption

A numeric standard is the concentration of a pollutant in water intended to achieve the beneficial use. Numeric standards reflect specific beneficial uses as adopted by the use classes (1-5). If not exceeded, numeric standards will protect the beneficial use. Numeric standards are not available for all pollutants and so are complemented through additional tools including, biological monitoring, to fully assess the beneficial use of aquatic community health. If a pollutant has numeric standards for more than one beneficial use class, the most stringent value applies.


Antidegradation protections maintain high quality waters from deterioration. Antidegradation will allow future generations to retain the highly valued recreational and aesthetic resources we enjoy, and ultimately save money. Preventing the degradation of surface waters is usually less costly than restoring already degraded waters.

Antidegradation provides three levels of protection for surface waters:

  1. Existing uses of the water body must be maintained and protected.
  2. High water quality (water quality better than the applicable water quality standard) must be maintained unless a lowering of water quality is necessary to accommodate important economic and social development.
  3. Exceptional characteristics of specific waters designated as outstanding, very sensitive, or unique resources -- called outstanding resource value waters or ORVWs (Minn. R. 7050.0335) -- must be maintained and protected. ORVWs are either "prohibited" or "restricted":
  • New or expanded discharges are banned in prohibited ORVWs, which include waters such as those within the Boundary Waters Canoe Area Wilderness and Voyageurs National Park.
  • New or expanded discharges are controlled in restriced ORVWs to maintain their exceptional characters. Examples of restricted ORVWs include portions of Lake Superior and federal and state designated scenic and recreational river segments such as the St. Croix River.
  • All surface waters in the Lake Superior basin are designated as outstanding international resource waters (OIRWs). Antidegradation protections for the Lake Superior basin focus on reducing the loading of bio-accumulative pollutants.

Protections similar to antidegradation also exist for groundwater, but are termed non-degradation. See Minn. R. 7060.0500 for further information. 

How to determine the uses a particular waterbody is protected for

To know which water quality standards apply to a particular waterbody, the beneficial use classifications must be known.

Two parts of Minn. R. ch. 7050 are important for determining the beneficial uses assigned to any water of the state:

  • Minn. R. 7050.0470 Classifications or listings for major waters in major surface water drainage basins
  • Minn. R. 7050.0430 Unlisted waters (also Minn. R. 7050.0425, classifies unlisted wetlands).

All surface waters are protected for aquatic life and recreation (Class 2), unless the waterbody has been individually assessed and re-classified, through rulemaking, as a limited resource value water (Class 7). Both Class 2 and Class 7 waters (i.e., all surface waters of the state) are also designated Class 3, 4A, 4B, 5 and 6, and are protected for the associated beneficial uses, as listed above (Minn. R. 7050.0400 to 7050.0470).  

Listed waters. Minnesota R. 7050.0470 is a listing, by major watershed, of individual waters and their associated use classifications. Only a limited subset of all waters is listed in Minn. R. 7050.0470. For example, waters that are individually listed include trout waters, surface waters protected for drinking, outstanding resource value waters, and Class 7 limited resource value waters. Minnesota R. 7050.0410 and 7050.0420 state the additional uses that all listed waters are protected for. It should be noted that the vast majority of surface waters are not listed (see “Unlisted waters,” below).

The listings in 7050.0470 are arranged by nine major Minnesota watersheds; rivers and streams are listed first, followed by lakes and wetlands, both in alphabetical order.

Unlisted waters. If the water of interest is not listed in Minn. R. 7050.0470, and again, most surface waters are not, then Minn. R. 7050.0430 applies. This short but very important part of the rule classifies all unlisted waters with multiple beneficial uses. These “unlisted” surface waters of the state are classified as Class 2B, 3C, 4A, 4B, 5, and 6 waters.

For wetlands, information on their classification is found in (or Minn. R. 7050.0425. They are specifically listed as for wetlands)(Class 2D, 3D, 4C, 5, and 6) waters.

Occasionally waters may go by more than one name. If in doubt about the classification of a waterbody of interest we suggest you consult MPCA staff listed in the Contacts tab.

Draft Technical Support documents

A key part of proposing new or revised WQSs is developing the technical foundation behind the narrative and numeric WQSs. MPCA develops this foundation based on review of scientific data, consideration of relevant rules, guidance, public comments, and consultation with topic experts at the U.S. Environmental Protection Agency (administrator of the CWA), other state agencies, Tribal Authorities, and academic researchers. The product of this review are topic-specific Technical Support Documents (TSDs) that will later be introduced in the rulemaking record as the supporting documents (exhibits) to the proposed rules and Statement of Need and Reasonableness (SONAR). The goal of publishing these documents prior to the official notice for proposing revised rules and SONAR is to obtain early comments and additional data to help MPCA refine and improve the basis for the proposed water quality standards.

TSDs are available on the following topics (note: not all topics being revised as part of the scope of this review have TSDs available):

Supporting Information for WQS

When MPCA adopts revised WQS into rule (Minnesota Rules Chapters 7050 and 7052) there are extensive technical and other documents cited as exhibits or included in the Statement of Need and Reasonableness (SONAR). The supporting information is available from the MPCA File Managers upon request. For recent rulemakings, this webpage provides important reference documents and citations for WQS users to find primary supporting information on the following WQS:

Eutrophication Standards for Lakes/Reservoirs and Rivers (final rule notices published in State Register, March 10, 2008, volume 32, pp. 1699-1728 and August 4, 2014, volume 39, pp. 154-6).

PDF icon Minnesota Lake Water Quality Assessment Report: Developing Nutrient Criteria, Third Edition (wq-lar3-01) (September 2005)

HTML icon Minnesota’s approach to lake nutrient criteria development  (2008)

PDF icon Minnesota Nutrient Criteria Development for Rivers (wq-s6-08) (January 2013)

PDF icon Mississippi River Pools 1 through 8 - Developing River, Pool and Lake Pepin Eutrophication Criteria (wq-s6-09) (September 2012)

PDF icon Lake Pepin Site Specific Eutrophication Criteria (wq-s6-10) (March 2011)

Binary Data Development of eutrophication criteria for Minnesota streams and river using multiple lines of evidence (June 2015)

Regionalization of Minnesota’s Rivers for Application of River Nutrient Criteria (December 2013)

Total Suspended Solid (TSS) (final rule notice published in State Register, August 4, 2014, volume 39, pp. 154-6)

PDF icon Aquatic Life Water Quality Standards Draft Technical Support Document for Total Suspended Solids (Turbidity) (wq-s6-11) (May 2011)

Human Health Methods Revision for Class 2 Chronic Standards and Criteria (final rule notice published in State Register, March 16, 2015, volume 39, pp. 1344-46)

PDF icon Human Health-based Water Quality Standards technical support document (wq-s6-12a) (June 2017)

MPCA contacts on water quality standards and rulemaking

Use classifications

Human health and aquatic life standards


Tiered aquatic life uses

Rule coordinator

Triennial standards review coordinator

Impaired waters list

Site-specific modified standards


More information on water quality standards